The present invention is directed to data storage devices, and particularly to locking mechanisms that hold an actuator assembly in place when power to a data storage device is turned off. More particularly, the present invention is directed to a single point magnetic contact latching assembly for magnetically positioning and parking the read/write head of a disk drive, the movements of which are controlled by an actuator assembly, at a predetermined location above the disk media to prevent damage to both the read/write head and the disk media during off-power conditions. While the following specification, including the Detailed Description of the Drawings, refers to a single read/write head and a single disk, the scope and spirit of the present invention are not limited to such a configuration. Rather, the present invention is suitable for use with any combination of multiple read/write heads and multiple disks.
Disk drives are used as data storage devices for long-term storage of large quantities of data. These devices appear in such forms as magnetic-medium hard drives, magnetic-medium "floppy" diskette drives, and optical CD ROM drives. Both magnetic-medium hard drives and optical CD ROM disks have much greater data storage capabilities than "floppy" diskettes. Although the present invention can be used for both CD ROM and "floppy" diskette drives, its primary intended use is with magnetic-medium hard drives in which a read/write head rests immediately above a disk during off-power conditions.
In magnetic-media hard disk drives, the disk is typically mounted on a rotating spindle that extends through its center. The disk has a large number of annular magnetic "tracks" on the surface thereof that provides a plurality of concentric memory locations for "bits" of data. The read/write head is mounted on an actuator assembly that can move and position the read/write head across the rotating surface of the disk. The read/write head "flies" over the surface of the disk on a cushion of air generated by the rotation of the disk spinning on the spindle. The read/write head is thus in close spaced proximity with the surfaces of the disk but not in contact with the magnetic coating on that surface.
Hard disk drives frequently incorporate a device for "parking" (or latching) the read/write head of the drive over a predetermined location on the disk when the hard disk drive experiences an off-power condition. "Parking" is done to help prevent data loss caused by physical shocks experienced during shipping or other movements of the disk drive during off-power conditions caused by the read/write head striking the surface of the disk. The terms "park" and "parking," as used in this application, refer to maintaining the position of the read/write head over a predetermined location, usually a "landing zone" annulus located on the inside or outside diameter of the disk. This "landing zone" does not have any data stored thereon.
Various types of "parking" (or latching) devices are used to lock the actuator assembly and the read/write head connected thereto in a predetermined position when power is off to the hard disk drive. Some drives utilize a spring-biased pivoting latch arm that holds the actuator assembly in a fixed position under the force of a spring during non-use of the disk. An electromagnet is used to initially lock and release the latch during operation of the disk drive. Other drives utilize air flow generated by the one or more spinning disks to release a spring-biased latch arm. See, for example, Anderson, U.S. Pat. No. 4,985,793, Voice Coil Actuated Disk Drive Parking Device with Magnetic Bias; Malek, U.S. Pat. No. 4,903,157, Electromagnet-Actuated Head Latching Apparatus; and Campbell, U.S. Pat. No. 4,692,829, Magnetically Biased Aerodynamically Released Integral Safety Latch For Rigid Disk Drive.
"Parking" devices that utilize spring-loaded electromagnets or solenoids to release the latch have the disadvantage of using elements such as wire coils that are expensive and difficult to implement because of space and tolerance requirements. In addition, electromagnetic "parking" devices require electrical power to be released during "power-up" of the disk drive. This use of power drains life from batteries of portable computers. Air actuated "parking" devices, on the other hand, have the disadvantage of potentially interfering with the air flow necessary for the read/write head to properly "fly". Also, the air flow in a disk drive only creates a relatively small release force that creates latching reliability problems for "parking" release because only a correspondingly, relatively small latching force can be applied, thus decreasing "parking" integrity.
Another means utilized by disk drives that avoids the above-described problems is purely magnetic "parking" to latch the actuator by magnetic attraction of and direct contact between a ferromagnetic portion of the actuator and a permanent magnet assembly. See, for example, Kelsic et al., U.S. Pat. No. 5,023,736, Magnetic Latch for Disk Drive Actuator; Casey et al., U.S. Pat. No. 4,890,176, Crash Stop and Magnetic Latch for a Voice Coil Actuator; and Casey et al., U.S. Pat. No. 4,947,274, Resiliently Mounted Crash Stop and Magnetic Latch for a Voice Coil Actuator. A potential drawback of magnetic latches is that during operation of the disk drive, the movement of the actuator may be adversely affected by the attraction of the ferromagnetic portion of the actuator and the magnet assembly, thereby creating problems with accurate actuator positioning. Another problem is that a potentially large force may be required to release the actuator assembly from the magnet assembly. Also, when the magnet assembly and ferromagnetic portion of the actuator make contact, portions of the magnet assembly may break off or become dislodged and damage the disk medium. This occurs because the magnets used in the magnet assemblies are generally made from brittle alloys, such as rare earth cobalt, or highly filled polymers that have magnetic particles captured in the matrices thereof. Finally, a potential tolerance problem with multi-point contact magnetic assembly designs exists. If the areas where the contacts are to occur are not precisely aligned, the assembly will not provide the required latch force range. Force ranges due to practical mechanical tolerances often exceed 800% in multi-point designs.
A magnetic "parking" device that avoids the problems associated with conventional magnetic "parking" devices would be a welcome improvement. As long as such device securely latches and locks the actuator assembly in a predetermined position when the power is off to the disk drive, then the opportunity for damage to the data stored on the disk or the read/write head due to physical shocks exerted on the hard disk drive will be kept to a minimum.
Accordingly, the present invention provides a single-point magnetic contact latch assembly for magnetically engaging a ferromagnetic strike plate portion of an actuator assembly to securely hold the actuator in a fixed position and thus "park" the read/write head in a predetermined location on the disk. A crash stop made of impact absorbing material, such as a resilient plastic, is provided that limits the movement of the actuator assembly in at least one of its directions of travel beyond a predetermined point. The single-point magnetic contact latch is mounted on the crash stop and magnetically engages the ferromagnetic strike plate on the actuator assembly when the actuator assembly nears one of two extreme positions. This magnetic coupling helps prevent movement of the read/write head away from the "landing zone" on the disk during non-use, so as to protect against damage to the read/write head or data stored on the disk.
The single-point magnetic contact latch includes a permanent magnet having opposite magnetic poles on opposing ends thereof. In one embodiment, the permanent magnet has a central bore extending axially therethrough. It is to be understood, however, that the permanent magnet may comprise of a plurality of pieces. A solid, ferromagnetic core extends through the bore of the magnet. A first end of the core extends beyond a first end of the magnet and forms the single-point contact which interacts with the actuator. The first end of the core may be substantially curvilinear in shape. The opposing second end of the core has an annular flange with a first face which abuts a second end of the magnet and a second face which abuts a substantially vertical portion of the crash stop to which the latch is mounted. A casing substantially surrounds the magnet. The casing is hollow with an axial length greater than the axial length of the magnet. The casing has an open end and a partially closed end. The partially closed end has an opening therein through which the first end of the core extends. The magnetic latch is assembled by axially disposing the core within the bore of the permanent magnet so that the first face of the flange abuts a second end of the magnet and the first end of the core extends through and beyond the first end of the magnet. The casing is placed over the permanent magnet so that the inner peripheral surface near the edge of the open end of the casing engages an outer peripheral surface of the annular flange with a press-fit so that the casing is outwardly radially deformed. The casing securely anchors the permanent magnet to the core and covers it so that portions thereof are protected from physical contact during handling and operation. This helps prevent portions of the magnet from falling off into the disk drive. This press-fit assembly has the additional advantage of eliminating the use of adhesives to fix the magnet in place. Adhesively mounted magnets suffer from an outgassing problem that can cause damage to components within the sealed disk drive. The magnetic latch assembly is directly press-fit mounted to the crash stop assembly via an integral pin axially extending from the second face of the annular flange.
When the actuator assembly moves towards one of two of its extreme positions, magnetic flux flows from the permanent magnet through the ferromagnetic core, through the ferromagnetic strike plate of the actuator assembly, and then returns to the permanent magnet through the other pole. This flux flow path results because ferromagnetic metal is a superior flux conductor compared to the surrounding air. The magnetic attraction between the magnetic latch assembly and the strike plate of the actuator assembly serves to latch the actuator in a predetermined fixed position and "park" the read/write head over an annularly, concentric, data-free "landing zone" on the disk of the disk drive.
The magnetic coupling force generated by the latch, although sufficient to latch the actuator assembly in position, is easily overcome when the actuator is driven during power-on conditions of the disk drive. Indeed, an object of the invention is to provide a relatively steep fall-off of magnetic-coupling force versus air-gap distance (distance between the single-point magnetic contact of the core and the ferromagnetic strike plate portion of the actuator assembly) such that the "reach-out" strength of the magnet assembly decreases rapidly as the distance from the contact point increases. When sufficient current flows through an armature of the actuator to overcome the magnetic attraction between the ferromagnetic strike plate of the actuator and the magnetic latch assembly, the actuator will need to move only a short distance to no longer be magnetically linked thereto. This eliminates the potential problem present in other designs in which movement of the actuator assembly during power-on conditions may be affected by attraction between the ferromagnetic portion of the actuator assembly and the magnetic latch assembly.
Other objects of the present invention include prevention of the aforementioned outgassing problem occurring when adhesives are used to retain the magnet. Also, complex and expensive electromagnetic components are eliminated. Finally, the single-point magnetic contact design overcomes force tolerance problems encountered in many conventional magnetic contact assemblies that rely on multiple contact points and one or more strike plates, both of which must be nearly perfectly aligned in order for the assembly to operate correctly and repeatably. That is, the use of a single-point magnetic contact magnetic latch assembly provides a smaller tolerance range of latch forces than that of multi-point magnetic contact latch assemblies.
In another embodiment of the present invention, a permanent magnet has opposing magnetic poles on opposing first and second ends thereof and a bore extending axially therethrough between the first and second ends. This magnet may be cylindrical, toroidal, or annular in shape and magnetized in an axial direction. The magnet may be unitary in construction or composed of a plurality of segments that are assembled together to form one of the above-described shapes.
A substantially spherically-shaped ferromagnetic core is disposed within the interior bore of the permanent magnet so that a portion of the core extends beyond the first end of the magnet to form a single-point magnetic contact with a ferromagnetic portion of an actuator assembly such as strike plate. The portion of the core extending beyond the first end of the magnet may be substantially curvilinear in shape.
A mounting structure is provided for mounting the magnetic latch assembly to a disk drive. The mounting structure has a first end that abuts the second end of the permanent magnet. A second end of the mounting structure may have a pin formed thereon for mounting to the disk drive. An edge of the second end of the mounting structure may be beveled to facilitate fixedly attaching the pin to the disk drive.
A casing substantially surrounds the magnet. The casing is hollow with an axial length greater than the axial length of the magnet. The casing has an open end and a partially closed end. The partially closed end has an opening therein through which a portion of the core extends when the casing is press-fit over the magnet, core, and at least a portion of the mounting structure. The magnet, core, and at least a portion of the mounting structure are disposed within the hollow of the casing so that an air gap exists between the magnet and the casing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.